Catalytic Characterization of Synthetic K+ and Na+ Sodalite Phases by Low Temperature Alkali Fusion of Kaolinite during the Transesterification of Spent Cooking Oil: Kinetic and Thermodynamic Properties

Abstract

The mineral raw Egyptian kaolinite was used as a precursor in the synthesis of two sodalite phases (sodium sodalite (Na.SD) and potassium sodalite (K.SD)) according to the low alkali fusion technique. The synthesized Na.SD phase demonstrates enhanced total basicity (6.3 mmol OH/g), surface area (232.4 m2/g), and ion exchange capacity (126.4 meq/100 g) compared to the K.SD phase (217.6 m2/g (surface area), 96.8 meq/100 g (ion exchange capacity), 5.4 mmol OH/g (total basicity). The catalytic performance of the two sodalite phases validates the higher activity of the sodium phase (Na.SD) than the potassium phase (K.SD). The application of Na.SD resulted in biodiesel yields of 97.3% and 96.4% after 90 min and 60 min, respectively, while the maximum yield using K.SD (95.7%) was detected after 75 min. Robust base-catalyzed reactions using Na.SD and K.SD as catalysts were suggested as part of an operated transesterification mechanism. Moreover, these reactions exhibit pseudo-first order kinetics, and the rate constant values were estimated with consideration of the change in temperature. The estimated activation energies of Na.SD (27.9 kJ.mol−1) and K.SD (28.27 kJ.mol−1) reflected the suitability of these catalysts to be applied effectively under mild conditions. The essential thermodynamic functions, such as Gibb’s free energy (65.16 kJ.mol−1 (Na.SD) and 65.26 kJ.mol−1 (K.SD)), enthalpy (25.23 kJ.mol−1 (Na.SD) and 25.55 kJ.mol−1 (K.SD)), and entropy (−197.7 J.K−1.mol−1 (Na.SD) and −197.8 J.K−1.mol−1 (K.SD)), display the endothermic and spontaneous nature of the two transesterification systems.